A second boy is in a serious condition in hospital after consuming an unknown substance.
The 15-year-old was taken to Ninewells Hospital in Dundee after taking unwell in Perth on Sunday.
His condition is described as serious but stable.
The incident comes after another 15-year-old boy was taken to hospital critically ill on Friday after allegedly taking a type of ecstasy tablet.
Police say the incidents are not related, but have warned of the dangers of taking drugs.
Chief Inspector Maggie Pettigrew, Local Area Commander for Perth said: “Our thoughts are with both these young boys who are currently receiving treatment in hospital. I would like to stress that both of these incidents are completely unconnected.
“Our message is clear, there is no safe way to take drugs – there is always a risk. The effects can be unpredictable and can cause serious harm or even death.
“Police Scotland continues to work with its partner agencies including health officials and Education and Children’s Services in connection with these investigations.”
Andy Reddick, a consultant in Emergency Medicine for NHS Tayside, echoed the police’s stance.
He said: “The clinical scenarios we see in the Emergency Department include life threatening organ failure, breathing difficulties, obstructed airways and injuries sustained because of extreme behavioural reactions.
“Patients are admitted to intensive care and high dependency units as well as our Emergency Department ward regularly due to illegal drug use and, unfortunately, people can die after arriving at hospital due to their level of toxicity from the substance they have taken.
“There is huge variation in the strength and content of drugs sold illegally as it is an unregulated industry. The amount of active drug in ecstasy tablets can be as much as five times higher in one tablet versus another. Even if you have taken a particular drug before with no major ill effects, this does not mean you will have the same response the next time you take it.
“There is no safe way to take drugs recreationally and the only way to ensure that you don’t come to harm from using drugs is not to use them.”